--- title: "Data logger with Bluetooth scatternet" subject: "Instrumentation II" chapter: 5 key: "semester_5/instrumentation_ii:bt-datalogger-scatternet" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/bt-datalogger-scatternet site: BCT Engineering --- # Data logger with Bluetooth scatternet Instrumentation II · Chapter 5: Data Acquisition And Transmission - Asked in: 2071 Chaitra, 10 marks - Video: [piconet and scatternet in bluetooth in hindi](https://www.youtube.com/watch?v=d139X3tEq_w) — Perfect Computer Engineer - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/bt-datalogger-scatternet - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-5 ## Question A data logger receives signals from a Bluetooth scatternet. The scatternet consists of three piconets and within each piconet there are four bluetooth devices. The piconets communicate within themselves and amongst each other using the master/slave protocol. (a) Describe an analog transmission mechanism to capture the blue tooth signals by the data logger. Draw a complete system block diagram. (b) Describe the master/slave protocol that is present in blue tooth piconets and scatternets. (c) Draw the scatternet topology depicting the scenario maintained in the question. Make sure you adhere to the rules of the masters/slave protocol. ## Short answer Capture with antenna, 2.4 GHz BPF, LNA, mixer driven by hop synthesiser, FM demod, and data slicer, then baseband controller and logger. Each piconet has a master that polls its slaves in TDD; bridge nodes connect piconets in a scatternet. With three piconets of one master and three slaves, bridges link adjacent piconets. ## Answer #### (a) Capturing the Bluetooth signals by the data logger Bluetooth transmits an analog radio signal in the 2.4 GHz band using GFSK (Gaussian frequency shift keying) with 1600 hops/s. The data logger uses an RF receiver (analog front end) followed by digital processing. ```text Antenna -> BPF 2.4 GHz -> LNA -> Mixer -> IF filter -> FM demod ^ | Hop synthesiser (follows hop sequence)| v Data slicer -> Baseband / link controller -> uP -> Memory (logging) \-> Display, USB/PC ``` Steps: the antenna and band-pass filter select the 2.4 GHz band; the LNA amplifies; the mixer, driven by a frequency synthesiser tuned according to the hop sequence, converts to an intermediate frequency; the FM discriminator recovers the baseband GFSK signal; a data slicer converts it to bits; the baseband controller recovers packets (access code, header, payload), and the microprocessor time-stamps and stores the data in the logger memory. #### (b) Master/slave protocol - Each piconet has one **master** and up to seven active **slaves**. The master's clock and address define the hopping sequence and timing. - Time division duplex with 625 us slots: the master transmits only in even slots and a slave replies in the next odd slot only if it was addressed (polled) by the master. - Slaves communicate only with their master, never directly with each other. - In a **scatternet**, a **bridge** device belongs to two piconets (slave in both, or master in one and slave in the other) and divides its time between them. A device cannot be the master of two piconets. #### (c) Scatternet topology (3 piconets, 4 devices in each) Each piconet = 1 master + 3 slaves. Piconets are joined through two bridge slaves: B12 (in piconet 1 and 2) and B23 (in piconets 2 and 3). Count: P1 = M1, S11, S12, B12; P2 = M2, B12, S21, B23; P3 = M3, B23, S31, S32. ```text S11 S12 S21 S31 S32 \ / \ \ / M1 ---- B12 ---- M2 ---- B23 ---- M3 [piconet 1] [piconet 2] [piconet 3] ``` All links are master-slave links (every line joins a master to a slave). The data logger sniffs all three piconets: it follows the hop sequence of each master in turn (or uses three receivers) and stores the packets. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the analog front end, what does the mixer driven by the hop synthesiser do? A. Amplifies the signal with low noise B. Slices the demodulated signal into bits C. Converts the hopping 2.4 GHz signal to a fixed intermediate frequency D. Stores the data in memory Answer: C. The synthesiser follows the hop sequence so the IF stays constant. (Key point: Receiver chain) 2. Which modulation do Bluetooth signals use and how is it recovered in the receiver? A. AM, recovered by an envelope detector only B. QAM, recovered by a decoder only C. PCM, recovered by an ADC D. GFSK, recovered by an FM discriminator and a data slicer Answer: D. The discriminator recovers baseband GFSK and the data slicer converts it to bits. (Key point: Modulation) 3. In the piconet protocol, when can a slave transmit? A. Only in the odd slot after being polled by the master B. Any time it has data C. Directly to any other slave D. Only in even slots, before the master Answer: A. The master transmits in even slots; a slave replies in the next odd slot only if addressed. (Key point: Master/slave rule) 4. How many active slaves can a piconet have? A. Up to 3 B. Up to 7 active slaves with one master C. Up to 15 D. Unlimited Answer: B. One master and up to seven active slaves. (Key point: Piconet size) 5. Which statement about a bridge device is right? A. It can be master of two piconets B. It belongs to only one piconet C. It belongs to two piconets, and cannot be master of both D. It lets slaves talk to each other directly Answer: C. A bridge is a slave in both or master in one and slave in the other. (Key point: Scatternet bridge) ## Related in Instrumentation II - [Data logging system for optical, satellite, Bluetooth](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adata-logging-three-schemes) — Instrumentation II, chapter 5 - [Master-slave 8085 bidirectional communication via 8255](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Abidirectional-8085-master-slave) — Instrumentation II, chapter 2 - [Data logger input scanner and conditioner design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adatalogger-three-transducers) — Instrumentation II, chapter 5 - [Bluetooth network topology](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Abt-topology) — Instrumentation II, chapter 5, asked 9× - [Data logger block diagram and operation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adl-block) — Instrumentation II, chapter 5, asked 6× - [Characteristics of a data logger](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adl-characteristics) — Instrumentation II, chapter 5, asked 6× ## Related in other subjects - [Short note: Client-Server and Master-Slave](https://www.bctengineer.com/question.md?key=semester_8%2Fbig_data_technologies%3Ashort-note-client-server-master-slave) — Big Data Technologies, chapter 1 - [Master-slave JK flip-flop](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Amaster-slave-jk) — Digital Logic, chapter 6 - [Analog communication block diagram; FDM of three signals](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-block-fdm-three-signals) — Communication Systems, chapter 5 - [Guided and other transmission media](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Atransmission-media-explain) — Computer Networks and Security, chapter 2, asked 3×